1. Field of the Invention
The present invention relates to a method of forming an overcoat layer, containing a hydrophobic functional group and a hydrophilic functional group, that omits a post-treatment process after the overcoat layer is formed. The present invention also relates to a method of producing a color filter substrate and to a color filter substrate and a liquid crystal display produced using the same.
2. Discussion of the Background
Liquid crystal displays (LCD) have been extensively used as flat panel display devices. A liquid crystal display includes a thin film transistor substrate on which pixel electrodes are formed, a color filter substrate on which a common electrode is formed, and a liquid crystal layer that is interposed between the thin film transistor substrate and the color filter substrate. The thin film transistor substrate and the color filter substrate face each other. The liquid crystal display displays an image by applying a voltage to the pixel electrodes and the common electrode to rearrange liquid crystal molecules of the liquid crystal layer so as to control the amount of optical transmittance of the liquid crystal layer.
The liquid crystal displays are divided into an Optically Compensated Birefringence (OCB) mode, a Patterned Vertical Alignment (PVA) mode, an In-Plane Switching (IPS) mode, an Advanced In-Plane Switching (A-IPS) mode and a Fringe Field Switching (FFS) mode, according to driving methods. In the OCB mode and the PVA mode, transparent conductive layers are formed on both the color filter substrate and the thin film transistor substrate. Meanwhile, in the IPS mode, the A-IPS mode, and the FFS mode, a transparent conductive layer is formed on only the thin film transistor substrate.
In a liquid crystal display that is driven in the IPS, A-IPS, FFS mode, or the like, the color filter substrate has black matrixes, color filters, and an overcoat layer. That is, unlike the color filter substrate of the liquid crystal display that is driven in the OCB or PVA mode, a transparent conductive layer that is formed between the overcoat layer and the alignment layer is eliminated.
The black matrix typically separates red, green, and blue color filters. On the color filter substrate, the red, green, and blue color filters are repeatedly formed with black matrixes at the boundaries thereof.
The overcoat layer is formed on the alternately formed color filters and the black matrix, in order to remove step height formed between them. In the IPS, A-IPS, FFS mode, or the like, after the overcoat layer is deposited, an alignment layer is provided on the overcoat layer, and liquid crystals are aligned on the alignment layer in a predetermined direction. Here, the alignment layer needs to be hydrophilic in order to align the liquid crystal molecules in the predetermined direction. At present, examples of a material for the alignment layer include polyimides capable of forming a hydrophilic layer.
In order to remove the step height after the color filters are formed, the overcoat layer needs to be uniformly coated on the color filters. To this end, the overcoat layer needs to have the same hydrophobicity as the color filters and the black matrix. Accordingly, a hydrophobic polymer material is used as a constituent component of the overcoat layer.
However, if the hydrophilic alignment layer is disposed on the hydrophobic overcoat layer, a repulsive force may be generated between the alignment layer and the overcoat layer. Accordingly, the alignment layer may be separated, and therefore, the alignment layer may be unstably formed. In order to remove the repulsive force, it is necessary to make the overcoat layer hydrophilic. Consequently, after the overcoat layer is deposited, the surface of the overcoat layer may be subjected to UV treatment or O2 ashing to make the surface hydrophilic. Thereafter, the alignment layer is formed.
However, the surface post-treatment, such as the UV treatment or O2 ashing, may complicate the process of producing the color filter substrate and reduce productivity. Further, the reduction in productivity may negatively affect the resultant liquid crystal display.